C/EBPß regulates multiple IL-1ß-induced human astrocyte inflammatory genes.

BACKGROUND: CCAAT enhancer-binding protein (C/EBP)ß regulates gene expression in multiple organ systems and cell types, including astrocytes in the central nervous system (CNS). Inflammatory stimuli, interleukin (IL)-1ß, tumor necrosis factor-α, human immunodeficiency virus (HIV)-1 and lipopolysaccharide induce astrocyte C/EBPß expression. C/EBPß is detectable in brains of Alzheimer's disease (AD), Parkinson's disease (PD) and HIV-1-associated dementia (HAD) patients, yet little is known about how C/EBPß contributes to astrocyte gene regulation during neuroinflammation. METHODS: The expression of 92 human inflammation genes was compared between IL-1ß-treated primary human astrocytes and astrocytes transfected with C/EBPß-specific small interfering (si)RNA prior to IL-1ß treatment for 12 h. Transcripts altered by>two-fold compared to control were subjected to one-way analysis of variance and Newman-Keuls post-test for multiple comparisons. Expression of two genes, cyclooxygenase-2 (COX-2) and bradykinin receptor B2 (BDKRB2) was further confirmed in additional human astrocyte donors. Astrocytes were treated with mitogen-activated protein kinase-selective inhibitors, then with IL-1ß for 12 or 24 h followed by COX-2 and BDKRB2, expression analyses. RESULTS: IL-1ß altered expression of 29 of 92 human inflammation genes by at least two-fold in primary human astrocytes in 12 h. C/EBPß knockdown affected expression of 17 out of 29 IL-1ß-regulated genes by>25%. Two genes relevant to neuroinflammation, COX-2 and BDKRB2, were robustly decreased and increased, respectively, in response to C/EBPß knockdown, and expression was confirmed in two additional donors. COX-2 and BDKRB2 mRNA remained altered in siRNA-transfected astrocytes at 12, 24 or 72 h. Inhibiting p38 kinase (p38K) activation blocked IL-1ß-induced astrocyte COX-2 mRNA and protein expression, but not IL-1ß-induced astrocyte BDKRB2 expression. Inhibiting extracellular-regulated kinase (ERK)1/2 activation blocked IL-1ß-induced BDKRB2 mRNA expression while increasing COX-2 expression. CONCLUSION: These data support an essential role for IL-1ß in the CNS and identify new C/EBPß functions in astrocytes. Additionally, this work suggests p38K and ERK1/2 pathways may regulate gene expression in a complementary manner to fine tune the IL-1ß-mediated astrocyte inflammatory response. Delineating a role for C/EBPß and other involved transcription factors in human astrocyte inflammatory response may lead to effective therapies for AD, PD, HAD and other neurological disorders.